TW201731148A - Gas diffusion electrode, microporous layer coating material and production method thereof - Google Patents

Abstract

This gas diffusion electrode comprises a microporous layer on at least one side of a conductive porous substrate, wherein the thickness of the gas diffusion electrode is 30-180 [mu]m and the thickness of the microporous layer is 10-100 [mu]m, and wherein, when the surface of the microporous layer is observed from 4000 fields of view with a 0.25 mm2 surface area, the number of fields of view of said 4000 fields of view in which the maximum height Rz is greater than or equal to 50 [mu]m is 0 to 5. Thus, a gas diffusion electrode is provided which both suppresses damage to the electrolyte membrane caused by the gas diffusion layer and gas diffusion properties of the gas diffusion layer, and which exhibits excellent performance as a fuel cell.

Description

Gas diffusion electrode, microporous layer coating and manufacturing method thereof

A fuel cell is a mechanism in which energy generated when hydrogen reacts with oxygen to form water, and is taken out as electric energy. Since the energy efficiency is high and the discharged matter is only water, it is expected to be popular as a clean energy source. The present invention relates to a gas diffusion electrode used in a fuel cell. In particular, a gas diffusion electrode used in a polymer electrolyte fuel cell used as a power source for a fuel cell vehicle or the like in a fuel cell, and a microporous layer coating material used therefor.

The electrode used in the polymer electrolyte fuel cell is disposed in a polymer electrolyte fuel cell between two separators. The electrode is disposed on both surfaces of the polymer electrolyte membrane, and has a structure in which a catalyst layer formed on the surface of the polymer electrolyte membrane and a gas diffusion layer formed outside the catalyst layer are formed. As an individual member of the electrode for forming a gas diffusion layer, the gas diffusion electrode is circulated on the market. The performance required for the gas diffusion electrode includes gas diffusibility, conductivity for collecting electric power generated by the catalyst layer, and drainage property for effectively removing moisture generated on the surface of the catalyst layer. In order to obtain such a gas diffusion electrode, generally, a conductive porous substrate having both gas diffusibility and conductivity is used.

Specifically, carbon fiber can be used as the conductive porous substrate. Carbon felt, carbon paper, carbon cloth, etc. Among them, carbon paper is preferred from the viewpoint of mechanical strength and the like.

When the conductive porous substrate is directly used as a gas diffusion electrode, the rough surface of the conductive porous substrate causes damage to the electrolyte membrane, and the fuel cell durability is lowered. Therefore, in order to prevent the decrease in durability, a layer called a microporous layer is provided on the conductive porous substrate. Since the microporous layer is a part of the gas diffusion electrode, gas diffusibility and conductivity are required, and it is required to contain conductive fine particles and have pores.

The microporous layer is obtained by coating, drying, and sintering a microporous layer coating material in which conductive fine particles are dispersed on a conductive porous substrate. Therefore, if a large foreign matter is present in the microporous layer coating material, there is a possibility that the crucible is coated. If a convex substance is formed on the surface of the coating film formed by the microporous layer coating material, the convex material may cause damage to the electrolyte membrane, or the generated water may be accumulated in the catalyst layer due to the convexity. The space generated by the interface with the microporous layer hinders gas diffusion (hereinafter, the phenomenon is referred to as overflow). Therefore, it is required to reduce foreign matter in the microporous layer coating material, and to perform dust removal of the manufacturing step in order to minimize dust and the like. However, if the foreign matter in the microporous layer coating is to be reduced, it is not sufficient to be dust-free. One of the reasons for this is agglomerates of conductive fine particles contained in the microporous layer coating material.

Here, it is conventional to apply a strong shearing force to the microporous layer coating for a long period of time, and it is attempted to reduce the agglomerates by improving the dispersibility (Patent Documents 1 and 2). However, if it is to reduce the agglomerates in the microporous layer coating When the dispersibility of the high microporous layer coating material is lowered, the viscosity of the microporous layer coating material is lowered, and when it is applied onto the conductive porous substrate, there is a problem that the conductive porous substrate is infiltrated. When the microporous layer penetrates into the conductive porous substrate, the surface roughness of the conductive porous electrode substrate cannot be reduced. Therefore, it is required to suppress penetration of the microporous layer into the conductive porous substrate. For this reason, a tackifier or the like is added to the microporous layer coating to attempt to control the fluidity (Patent Document 3).

[Previous Technical Literature] [Patent Literature]

Patent Document 1: Japanese Patent Laid-Open Publication No. 2003-100305

Patent Document 2: Japanese Patent Laid-Open No. Hei 11-273688

Patent Document 3: Japanese Laid-Open Patent Publication No. 2015-138656

As a result of the investigation by the present inventors, it has been found that in order to reduce the dispersibility of the microporous layer coating material in order to reduce the aggregate in the microporous layer, penetration into the conductive porous substrate cannot be suppressed. Therefore, the gas diffusion electrode system produced by the techniques disclosed in Patent Documents 1 to 3 is difficult to attempt to suppress damage to the electrolyte membrane and gas diffusibility.

SUMMARY OF THE INVENTION An object of the present invention is to overcome the disadvantages of the prior art and to provide a gas diffusion electrode which exhibits good performance as a fuel cell while suppressing damage to an electrolyte membrane and gas diffusibility.

In order to solve this problem, the present invention employs the following means.

A gas diffusion electrode is a gas diffusion electrode having a microporous layer on at least one surface of a conductive porous substrate, wherein the gas diffusion electrode has a thickness of 30 μm or more and 180 μm or less, and the microporous layer has a thickness of 10 μm or more and 100 μm or less. When the surface of the microporous layer is observed with an area of 0.25 mm ² and 4000 fields of view, the number of fields of view having a maximum height Rz of 50 μm or more in the 4000 fields of view is 0 or more fields and 5 fields or less.

Further, the present invention comprises a microporous layer coating comprising a microporous layer coating containing conductive fine particles and a solvent, and the surface of the coating film formed by coating the microporous layer coating on a glass substrate to observe 2000 fields of view in an area of 0.25 mm ² In the 2000 field of view, the field of view with a maximum peak height Rp of 10 μm or more is 0 or more and 25 or less, and the gloss is 1% or more and 30% or less.

Furthermore, the present invention comprises a method for producing the microporous layer coating, which comprises a step of wetting and dispersing the conductive fine particles in a solvent, a step of dispersing, and a step of pulverizing the agglomerates in the coating obtained by the wetting and dispersing step. The comminution step.

By using the gas diffusion electrode of the present invention, it is possible to reduce the damage to the electrolyte membrane and the gas diffusibility, and it is therefore possible to provide a fuel cell having excellent durability and power generation performance.

1‧‧‧ crack

201‧‧‧ paint

202‧‧‧cutting section

203‧‧‧Rolling direction of the drum

204‧‧‧Minimum clearance

205‧‧‧Roller

301‧‧‧ device front

302‧‧‧ side of the device

303‧‧‧Rotor rotation direction

304‧‧‧ paint

305‧‧‧cutting section

306‧‧‧Rotor

307‧‧‧stator

401‧‧‧Flow Controller

402‧‧‧Pipe A

403‧‧‧Valve 1

404‧‧‧pressure controller

405‧‧‧Valve 2

406‧‧‧pipe B

407‧‧‧Air chamber A

408‧‧‧ gas diffusion electrode sample

409‧‧‧Air Chamber B

410‧‧‧Line C

411‧‧‧Gas Flowmeter

412‧‧‧ Sealing material

413‧‧‧Nitrogen

[Fig. 1] A crack in the surface of the microporous layer.

[Fig. 2] Schematic diagram of one aspect of the apparatus used in the pulverization step.

[Fig. 3] Schematic diagram of other aspects of the apparatus used in the pulverization step.

[Fig. 4] A schematic view of an apparatus for measuring gas diffusibility in a planar direction.

[Formation of the Invention]

In a polymer electrolyte fuel cell, a gas diffusion electrode requires high gas diffusibility for diffusing a gas supplied from a separator to a catalyst, high drainage for discharging water generated by an electrochemical reaction to a separator, and use High conductivity with the current drawn.

The gas diffusion electrode of the present invention is a gas diffusion electrode having a microporous layer on at least one surface of a conductive porous substrate. The gas diffusion electrode may have a microporous layer on only one side or a microporous layer on both sides, but it is more preferable to have a microporous layer only on one side.

The conductive porous substrate requires conductivity, gas diffusibility, drainage, and the like. The conductive porous substrate is preferably a porous substrate containing carbon fibers such as carbon fiber woven fabric, carbon fiber papermaking body, carbon fiber nonwoven fabric, carbon felt, carbon paper, carbon cloth, or the like; foamed sintered metal, metal mesh, and Expanding a porous metal substrate such as a metal plate. Among them, from the viewpoint of excellent corrosion resistance, the conductive porous substrate is preferably a carbon felt-containing carbon felt, carbon paper, carbon cloth or the like. Further, from the viewpoint of the characteristic of dimensional change in the thickness direction of the absorbing electrolyte membrane, that is, the "elasticity" is excellent, it is suitable to use a carbon fiber papermaking body as a substrate formed by carbide bonding, that is, carbon paper. The thickness of the conductive porous substrate is preferably 20 μm or more and 170 μm or less, and more preferably 50 μm or more and 170 μm or less. under.

Next, the microporous layer will be described. The microporous layer is a layer obtained by coating, drying, and sintering a microporous layer coating in which a conductive fine particle is dispersed in a solvent on a conductive porous substrate. Since the microporous layer is also a part of the gas diffusion electrode, the microporous layer is required to have conductivity, gas diffusibility, drainage, and the like as well as the conductive porous substrate. The average pore diameter of the microporous layer is preferably 0.01 μm or more and 5 μm or less.

In order to impart conductivity, the microporous layer contains conductive fine particles. Examples of the conductive fine particles used in the microporous layer include metal fine particles such as gold, silver, copper, platinum, titanium, titanium oxide, and zinc oxide, or metal oxide fine particles; and carbon material fine particles such as carbon black, graphene, and graphite; Vapor-grown carbon fiber (VGCF), carbon nanotube, carbon nanohorn, nano spiral carbon tube, stacked cup carbon nanotube, bamboo-shaped carbon nanotube, "conductive material with linear portion", Linear carbon such as graphite nanofibers and staple fibers of carbon fibers. The average of the longest diameter of the conductive fine particles is preferably 0.01 μm or more and 1000 μm or less.

Further, in order to efficiently discharge water generated during power generation for the purpose of water repellency of the microporous layer, the microporous layer preferably further contains a water repellent resin. Examples of the water repellent resin include polytetrafluoroethylene (PTFE), tetrafluoroethylene, hexafluoropropylene copolymer (FEP), perfluoroalkoxy fluororesin (PFA), polychlorotrifluoroethylene (PCTFE), and ethylene. ‧Tetrafluoroethylene copolymer (ETFE), ethylene ‧ chlorotrifluoroethylene copolymer (ECTFE) and fluororesin such as polydifluoroethylene (PVdF). From the viewpoint of high water repellency, the water repellent resin is preferably PTFE or FEP.

Moreover, in order to disperse the conductive fine particles in the solvent, micro The porous layer coating is also preferably a surfactant. In addition, the microporous layer coating means a coating material for forming a microporous layer using conductive fine particles and a solvent as essential components. As the surfactant for such purposes, polyethylene glycol mono-p-isooctylphenyl ether and polyoxyethylene lauryl ether are preferably used.

In order to prevent damage to the electrolyte membrane on the rough surface of the conductive porous substrate, it is preferred to form a microporous layer having a thickness of 10 μm or more on the surface of the conductive porous substrate. Therefore, the viscosity of the microporous layer coating is preferably 2 Pa ‧ or more, more preferably 5 Pa ‧ or more. When the viscosity of the microporous layer coating liquid is less than this, the coating liquid flows on the surface of the conductive porous substrate, and the pores of the conductive porous substrate flow into the coating liquid to cause penetration into the back surface. On the other hand, if the viscosity is too high, the coatability is lowered, so that the viscosity of the microporous layer coating is preferably 15 Pa‧s or less.

As a result of research by the inventors, it has been found that when a microporous layer coating having improved dispersibility is applied to a conductive porous substrate in order to reduce aggregates, as shown in Fig. 1, a large crack 1 is generated. The characteristics of the conductive fine particles are not primary particles, but primary aggregates in which primary particles are agglomerated, secondary aggregates in which the primary aggregates are further agglomerated, and tertiary aggregates in which the secondary aggregates are further agglomerated. Aggregates of size exist in a distribution of peaks in a certain size range. When the conductive fine particles are dispersed in a solvent, the improvement in dispersibility means that the aggregate size distribution shifts in a small direction. The aggregate of the conductive fine particles whose size is reduced in size and thus reduced in size is weak, and the stress generated by the thermal expansion during drying and sintering causes the aggregation of the aggregate to disappear, and cracks occur in the microporous layer. In other words, the production of cracks on the microporous layer It can be used as an indicator of the dispersion of microporous coatings. The microporous layer coating used in the present invention is preferably not too dispersible. Therefore, the gas diffusion electrode of the present invention preferably has a crack occupying ratio of 0% or more and 0.072% or less on the surface of the microporous layer. The crack occupying ratio on the surface of the microporous layer is more preferably 0% or more and 0.035% or less, further preferably 0% or more and 0.0072% or less, and particularly preferably 0% or more and 0.00072% or less.

Further, as a result of research by the inventors, it has been found that the dispersibility of the microporous layer coating is correlated with the glossiness, and the dispersibility is improved to increase the gloss. Here, the glossiness is a value obtained by measuring the surface of the microporous layer formed by coating the microporous layer coating on a glass substrate by using a glossiness measuring device. The detailed measurement method will be described later. As described above, when the conductive fine particles are dispersed in the solvent, if the dispersibility is improved, the size distribution of the aggregates is shifted in a small direction. Therefore, it is considered that the peak shift of the size of the aggregate appears as a change in gloss. Gloss is the reflectance of light irradiated at an angle, and therefore the surface roughness of the coating film formed by the microporous layer coating is an important factor. The surface roughness of the coating film formed by the microporous layer coating is considered to be related to the peak position of the aggregate size distribution. If the peak position of the aggregate size distribution is located in a larger portion, the surface of the coating film formed using the microporous layer coating is rough, and as a result, the gloss is lowered. On the other hand, if the peak position is located in a smaller portion, the surface of the microporous layer formed using the microporous layer coating is smoother, and as a result, the gloss is improved. In other words, the gloss can be used as an indicator of the dispersibility of the microporous layer coating.

As a result of research by the inventors and the like, it has been found that if the dispersibility of the microporous layer coating is excessively increased, the microporous layer coating will be more conductive. Infiltration of the porous substrate. The reason for this is considered to be that, as a result of the improvement in dispersibility, the aggregate size of the conductive fine particles is reduced, and the aggregates fall into the pores of the conductive porous substrate.

From the above, in order to suppress the infiltration of the microporous layer which is mainly caused by the decrease in gas diffusibility to the conductive porous substrate, the glossiness of the microporous layer coating of the present invention is about the glossiness indicating the dispersibility index of the microporous layer coating material. 30% or less, preferably 20% or less. Further, if the gloss is too low, the surface smoothness will be lost. Therefore, the microporous layer coating of the present invention has a gloss of 1% or more.

Further, when the aggregate of the conductive fine particles in the microporous layer coating material is too large, the electrolyte membrane is damaged and overflow occurs. Therefore, when the microporous layer coating of the present invention observes 2000 fields of view on the surface of the microporous layer coated on the glass substrate at an area of 0.25 mm ² , the number of fields of view having a maximum peak height Rp of 10 μm or more in the 2000 field of view is 0 or more. Below the visual field, it is preferably 0 or more fields and 5 fields or less, and more preferably 0 field of view. The detailed measurement method of Rp will be described later.

In addition, when the maximum height Rz of the surface of the microporous layer formed on at least one surface of the conductive porous substrate is 50 μm or more due to the aggregate of the conductive fine particles, the electrolyte membrane is damaged and overflows. Therefore, in the gas diffusion electrode of the present invention, when the surface of the microporous layer is observed at an area of 0.25 mm ² for 4000 fields, the number of fields of view having a maximum height Rz of 50 μm or more in the 4000 field of view is 0 or more fields and 5 fields or less, preferably 0 field of view. The detailed measurement method of Rz will be described later.

Further, when the microporous layer coating material is applied to the conductive porous substrate, the coating preferably has no shaking property for the convenience of handling. (thixotropy) or negative thixotropy. Here, in the case of shearing, when the shear is applied to the paint, the viscosity in the appearance is temporarily lowered, and even after the shearing is stopped, the viscosity is maintained for a certain period of time, and when the rheological measurement is performed, the hysteresis curve is drawn. Further, the negative shake degeneration is such that when shear is applied to the paint, the viscosity in appearance is temporarily increased, and even after the shearing is stopped, the viscosity is maintained for a certain period of time, and when the rheological measurement is performed, a hysteresis curve is drawn.

The step of producing the microporous layer coating material preferably has a step of wetting the conductive fine particles with a solvent (mixed with a solvent), dispersing (hereinafter referred to as a wetting/dispersing step), and a coating obtained by the wetting and dispersing step. The step of pulverizing the agglomerate (hereinafter referred to as a pulverization step).

Examples of the apparatus used in the wetting and dispersing step include a stirring and mixing device, a self-rotating agitating mixer, a kneading extruder, a powder suction type continuous dissolving and dispersing device, a homogenizer, a vertical solid-liquid mixing machine, and a horizontal solid-liquid mixing machine. The conductive fine particles and the solvent can be used if they are wettable or dispersible.

In the pulverization step, in order to apply shear to the coating material more effectively, the viscosity of the coating material after the wetting, the dispersion step, and the pulverization step is preferably 5 Pa ‧ or more, more preferably 10 Pa ‧ s or more. On the other hand, if the viscosity is too high, the coating is excessively sheared during the pulverization step, and the dispersion is excessively performed. Therefore, the viscosity of the coating after the wetting, the dispersion step, and the pulverization step is preferably 300 Pa‧s or less, more preferably It is 100 Pa‧s or less, and further preferably 40 Pa‧s or less.

Preferably, the apparatus used in the pulverizing step uses the apparatus as shown in Figs. 2 and 3. Figure 2 is reversed by two rollers (205) Rotating (203) causes the coating (201) to enter the minimum gap (204) of the drum and is sheared to comminute the agglomerates in the coating (201). At this time, the portion to which the shear is applied is referred to as a shearing portion (202). The apparatus having the configuration of Fig. 2 is called a three-roll mill. Figure 3 is a rotation of the rotor (306) and the coating (304) between the stator and the stator (307) will be sheared to comminute the agglomerates in the coating (304). At this time, the portion to which the shear is applied is referred to as a shearing portion (305). The apparatus having the configuration of Fig. 3 is referred to as a mediumless grinder. In order to pulverize the aggregate in the coating, the minimum gap of the sheared portions (202 and 305) is preferably 500 μm or less, more preferably 300 μm or less, further preferably 100 μm or less. If the minimum gap is too small, the dispersion of the coating proceeds continuously, so the minimum gap of the sheared portion is preferably 10 μm or more, more preferably 20 μm or more.

Further, in order to suppress excessive dispersion of the coating material, the shearing portion of the shearing portion of the apparatus for pulverizing is preferably more than 0 second and less than 5 seconds, more preferably greater than 0 second and 1 second in the minimum gap portion. the following. In addition, even in the case where the coating passes through the apparatus for pulverizing a plurality of times and passes through the minimum gap portion of the shearing portion of the apparatus for pulverizing, the so-called "minimum of the shearing portion of the apparatus for pulverizing" The residence time of the paint in the gap portion means the residence time of one pass, and does not indicate the total value of the plurality of times.

Further, in order to suppress excessive dispersion of the paint, the apparatus for pulverization is preferably one pass. Here, the means for pulverizing is one pass, which means that the coating passes through the apparatus for pulverizing once, and the coating material passes through the structure of the minimum gap portion of the shearing portion once. In order to obtain the most appropriate coating characteristics, the microporous layer coating may also be passed through the apparatus for pulverization (Figs. 2 and 3).

Further, in the apparatus for pulverizing, the shearing speed of the shearing portion is preferably 1000 s ^-1 or more and 1,000,000 s ^-1 or less. Here, the shearing speed is a value obtained by multiplying the minimum gap distance (m) of the shearing portion of the apparatus for pulverizing with the peripheral speed (m/s) of the drum or rotor of the shearing portion.

The apparatus for the pulverization step is a device having the above-described features, and specifically, a three-roll mill and a medium-free grinder can be used.

The application of the microporous layer coating liquid to the conductive porous substrate can be carried out using various commercially available coating apparatuses. Specifically, screen printing, roll screen printing, spray, gravure printing, gravure printing, die coating, coating bar coating, blade coating, and comma blade coating can be used. From the viewpoint of quantifying the coating amount without being affected by the surface roughness of the conductive porous substrate, it is preferably applied by a die coater. Further, when the fuel cell stack is filled with the gas diffusion electrode, it is preferable to apply the coating by a knife coater or a comma knife coater in order to improve the smoothness of the coated surface in order to improve adhesion to the catalyst layer. The coating methods exemplified above are merely illustrative and are not necessarily limited to the methods.

The microporous layer may be a single layer or a plurality of layers, and particularly preferably a first microporous layer contacting the conductive porous substrate and a second microporous layer contacting the first microporous layer and located on the outermost surface of the gas diffusion electrode. The layer is composed. When the gas diffusion electrode having the first microporous layer and the second microporous layer is produced, it is preferred to apply a first microporous layer coating liquid on the surface of the conductive porous substrate side, and then apply the coating layer. 2 microporous layer coating solution.

In the multilayer coating, a first microporous layer coating liquid is applied by a die coater, and a second microporous layer coating liquid is further applied by a die coater; 1 Coating of the microporous layer coating liquid, coating of the second microporous layer coating liquid by a die coater; coating of the first microporous layer coating liquid by a comma knife coater, and performing the second coating by a die coater a method of coating a microporous layer coating liquid; a method of applying a first microporous layer coating liquid by a lip coater, applying a second microporous layer coating liquid by a die coater; and using a swash plate type die The coating machine is a method in which the first microporous layer coating liquid and the second microporous layer coating liquid are overlapped and applied before the substrate coating. In particular, in order to uniformly apply a coating liquid having a high viscosity, the coating of the first microporous layer coating liquid is preferably carried out by a die coater or a comma knife coater.

After the application of the microporous layer coating liquid, the dispersion medium of the microporous layer coating liquid (water is water) is dried and removed as needed. When the dispersion medium is water, the drying temperature is preferably room temperature (about 20 ° C) to 150 ° C or lower, and more preferably 60 ° C or higher and 120 ° C or lower. Drying of the dispersion medium can also be carried out in the subsequent sintering step.

After the application of the microporous layer coating liquid, the surfactant used in the microporous layer coating liquid is removed, and the water repellent resin is once dissolved to form conductive fine particles, and sintering is generally performed.

The sintering temperature varies depending on the boiling point or decomposition temperature of the surfactant to be added, but is preferably from 250 ° C to 400 ° C. When the sintering temperature is less than 250 ° C, the removal of the surfactant cannot be sufficiently achieved, or it takes a long time to completely remove it. If the sintering temperature exceeds 400 ° C, decomposition of the water-repellent resin may occur.

The sintering time should be as short as possible from the viewpoint of productivity, preferably within 20 minutes, more preferably within 10 minutes, further preferably within 5 minutes. If the sintering time is too short, the surfactant is removed. It is not possible to carry out the problem sufficiently, and there is a problem that the water-repellent resin is not sufficiently dissolved, and therefore it is preferably 10 seconds or more.

The temperature and time of sintering can be determined by selecting the most suitable temperature and time by considering the melting point or decomposition temperature of the water-repellent resin and the decomposition temperature of the surfactant.

Since the gas diffusion electrode is required to have excellent gas diffusibility, the gas diffusibility in the thickness direction is preferably 30% or more, more preferably 30% or more and 50% or less, still more preferably 30% or more and 40% or less. The method of measuring the gas diffusibility in the thickness direction will be described later.

In order to achieve the gas diffusion performance in the thickness direction, the thickness of the gas diffusion electrode is 180 μm or less, preferably 150 μm or less, and more preferably 130 μm or less. Since the strength is lowered by being too thin, the thickness of the gas diffusion electrode is 30 μm or more, preferably 40 μm or more.

Further, as described above, the microporous layer has a thickness of 10 μm or more, preferably 20 μm or more. On the other hand, if the thickness is too large, the gas diffusibility in the thickness direction is lowered. Therefore, the thickness of the microporous layer is 100 μm or less, preferably 50 μm or less.

Further, even if the thickness of the microporous layer is ensured, when the microporous layer penetrates into the conductive porous substrate, the gas diffusibility in the planar direction may be hindered. The gas diffusibility in the plane direction of the gas diffusion electrode is preferably 0.7e ^0.025x cc/min or more, and more preferably 0.7, when x (μm) is the thickness of the gas diffusion electrode and e is Napier's constant. e ^0.025x cc/min or more and 200 cc/min or less, particularly preferably ^{0.7e 0.025x} cc/min or more and 150 cc/min or less. When the gas diffusibility in the planar direction is less than the above range, the gas utilization efficiency in the fuel cell is lowered, and the power generation performance of the fuel cell may be lowered. The method of measuring the gas diffusibility in the plane direction will be described later. In order to make the gas diffusibility in the plane direction to be 0.7e ^0.025x cc/min or more, it is necessary to suppress penetration of the conductive porous substrate into the microporous layer, and ^{apply the} microporous layer coating produced by the above method to form a microporous layer. It is valid.

In order to reduce the agglomerates on the surface of the microporous layer and suppress the generation of cracks on the surface of the microporous layer, and further ensure gas diffusion in the planar direction, the microporous layer preferably has a first microporous layer contacting the conductive porous substrate and The second microporous layer is in contact with the first microporous layer and located on the outermost surface of the gas diffusion electrode. By producing the first microporous layer by the above method, it is possible to reduce the aggregate in the first microporous layer, suppress the occurrence of cracks, and suppress the infiltration into the conductive porous substrate. Even if the second microporous layer is produced by high dispersion by a conventional method, if the surface of the first microporous layer is smooth and the thickness is thin, cracks do not occur, and the second microporous layer can be filled by the first microporous layer. Since the layer does not penetrate into the conductive porous substrate, it is possible to reduce the aggregation of the surface of the microporous layer, suppress the occurrence of cracks, and ensure gas diffusion in the planar direction.

When the microporous layer has a multilayer structure, the effect of preventing the roughness of the conductive porous substrate from being transferred to the electrolyte membrane to cause physical damage to the electrolyte membrane, the total thickness of the microporous layer is preferably 10 μm or more. More preferably, the thickness of the first microporous layer itself is 9.9 μm or more, more preferably 10 μm or more, and still more preferably 19.9 μm or more. However, the thickness of the first microporous layer is preferably less than 100 μm from the viewpoint of ensuring gas diffusibility even if the second microporous layer is laminated thereon.

The thickness of the second microporous layer is preferably 0.1 μm or more and less than 10 μm. When the thickness of the second microporous layer is less than 0.1 μm, since the second microporous layer cannot completely cover the surface of the first microporous layer, when the first microporous layer has agglomerates or cracks, it will appear on the surface of the microporous layer. . Further, when the thickness of the second microporous layer is 10 μm or more, cracks are formed on the surface of the microporous layer. The thickness of the second microporous layer is preferably 7 μm or less, more preferably 5 μm or less.

[Examples]

Hereinafter, the materials used in the examples of the present invention, the method for producing the gas diffusion electrode, the method for producing the microporous layer coating, the method for evaluating the gas diffusion electrode, and the method for evaluating the microporous layer coating are specifically described below by way of examples.

<material>

A: Conductive porous substrate

(1) A carbon paper having a thickness of 100 μm and a porosity of 85% was prepared in the following manner.

First, carbon fiber paper is produced by the following papermaking steps. Polyacrylonitrile-based carbon fiber "TORAYCA" (registered trademark) T300-6K (average single fiber diameter: 7 μm, number of single fibers: 6000) manufactured by TORAY Co., Ltd. was cut into a length of 6 mm, and water was used as a papermaking medium together with pulp. After continuous drawing, the obtained sheet was further immersed in a 10% by mass aqueous solution of polyvinyl alcohol, and then an elongated carbon fiber paper was continuously produced by drying, and wound up into a roll shape. The carbon fiber paper obtained had a basis weight of 15 g/m ² , and the amount of pulp was 40 parts by mass based on 100 parts by mass of the carbon fibers, and the amount of polyvinyl alcohol adhered was 20 parts by mass.

Next, the phenol resin is made by the following resin impregnation step It is impregnated with the carbon fiber paper obtained by the foregoing. A flaky graphite (average particle diameter: 5 μm, aspect ratio: 15), a dispersion of phenol resin and methanol in a mass ratio of 2:3:25 were prepared. The dispersion was continuously impregnated into the carbon fiber paper with a resin impregnation amount of 78 parts by mass based on 100 parts by mass of the carbon fiber, and dried at a temperature of 90 ° C for 3 minutes, and then wound up into a roll to obtain a resin. Impregnated with carbon fiber paper. The phenol resin was mixed with a resol type phenol resin and a novolac type phenol resin in a mass ratio of 1:1. The carbonization yield of the phenol resin (a mixture of a resol type phenol resin and a novolac type phenol resin) was 43%.

The heating plate was placed in a parallel molding manner on the press molding machine, and the separator was placed on the lower heating plate, and the opening of the press was repeated at a heating plate temperature of 170 ° C and a surface pressure of 0.8 MPa. The resin-impregnated carbon fiber paper obtained as described above was sandwiched between the release paper, and intermittently conveyed by the press machine, and the resin impregnated carbon fiber paper was subjected to compression treatment, and then wound up into a roll shape.

The carbon fiber paper was subjected to compression treatment as a precursor fiber sheet, and carbon paper was obtained by the following carbonization step. In a heating furnace maintained at a nitrogen atmosphere and having a maximum temperature of 2400 ° C, a precursor fiber sheet is introduced and continuously moved in a heating furnace at about 500 ° C / min (400 ° C / min before reaching 650 ° C, and the temperature exceeds 650 ° C) Then, after firing at a temperature increase rate of 550 ° C /min), the coil was taken up in a roll shape to obtain carbon paper. The obtained carbon paper had a density of 0.25 g/cm ³ , a porosity of 85%, and an average pore diameter of 40 μm.

(2) The thickness was 200 μm, the porosity was 85%, and the average pore diameter was obtained in the same manner as in the above (1) except that the weight per unit area of the carbon fiber and the thickness of the separator during the compression treatment were adjusted to be 200 μm. 40 μm carbon paper.

B: Conductive microparticles

Carbon black 1 (hereinafter referred to as CB1) (DBP oil absorption 175 cc / 100 g, BET specific surface area 67.4 m ² / g, average particle size 35 nm)

Carbon black 2 (hereinafter referred to as CB2) (DBP oil absorption 140cc/100g, BET specific surface area 43.1m ² /g, average particle diameter 50nm)

Gas-phase carbon fiber "VGCF" (registered trademark) (a conductive material having a linear portion, having an average fiber diameter of 150 nm, an average fiber length of 9 μm, and a specific surface area of 13 m ² /g).

C: solvent

purified water

D: surfactant

Polyethylene glycol mono-p-isooctylphenyl ether "TRITON X-100" (registered trademark) (manufactured by Sigma-Aldrich Co., Ltd.)

E: water-repellent resin

PTFE dispersion "POLYFLON D-210C" (registered trademark) (manufactured by DAIKIN Industrial Co., Ltd.)

FEP dispersion "POLYFLON ND-110" (registered trademark) (manufactured by DAIKIN Industrial Co., Ltd.).

<Measurement of Thickness of Conductive Porous Substrate, Microporous Layer, and Gas Diffusion Electrode>

The thickness of the gas diffusion electrode and the conductive porous substrate was measured using a digital thickness gauge "DIGIMICRO" manufactured by Nikon Co., Ltd., and a load of 0.15 MPa was applied to the substrate.

In addition, regarding the thickness of the microporous layer, a scanning electron microscope (S-4800, manufactured by Hitachi, Ltd.) was used. The vertical cross section of the diffusion electrode (the cross section in the thickness direction) determines the interface between the conductive porous substrate and the microporous layer (the interface referred to herein is the portion where the outermost surface of the electrically porous substrate is in contact with the microporous layer). The portion where the microporous layer penetrates into the conductive porous substrate is not included, and the distance between the interface and the surface of the microporous layer is determined as the thickness of the microporous layer. The measurement was performed in 10 fields of view, and the average value was obtained. When a cross section of the gas diffusion electrode was produced, an ion milling apparatus IM4000 manufactured by Hitachi High-Technologies Co., Ltd. was used. The magnification of the scanning electron microscope image in the measurement was measured at 1000 times or 2000 times.

<Gas diffusivity in the thickness direction of the gas diffusion electrode>

The gas diffusion, water vapor diffusion and penetration performance measuring device (MVDP-200C) of the West China Industrial Co., Ltd. are used to circulate oxygen on the gas diffusion electrode side (primary side) and the other side (secondary side). Nitrogen. The pressure difference between the primary side and the secondary side is controlled to be around 0 Pa (0 ± 3 Pa). In other words, there is almost no gas flow caused by the pressure difference, and gas movement occurs only by molecular diffusion. The oxygen concentration at the time of equilibrium was measured by a gas concentration meter on the secondary side, and this value (%) was used as an index of gas diffusibility in the thickness direction.

<Gas diffusivity in the planar direction of the gas diffusion electrode>

Using the Xihua Industrial Gas Diffusion ‧ Water Vapor Diffusion ‧ Penetration Performance Measuring Device (MVDP-200C), in the piping system as shown in Figure 4, initially only valve A (403) is opened and valve B ( 405) In the off state, nitrogen gas (413) is circulated in the primary side line A (402), and the mass flow controller (401) is adjusted to flow a predetermined amount (190 cc/min) of gas to subject the pressure controller (404) to the gas. The pressure system is 5 kPa with respect to atmospheric pressure. On the sealing material (412) between the gas chamber A (407) and the gas chamber B (409), a gas is arranged as shown Diffusion electrode sample (408). Next, valve A (403) is closed, valve B (405) is opened, and nitrogen is circulated in line B (406). The nitrogen gas flowing into the gas chamber A (407) is moved to the gas chamber B (409) through the gas diffusion electrode sample (408), passes through the line C (410), and is discharged to the atmosphere through the gas flow meter (411). The gas flow rate (cc/min) flowing through the gas flow meter (411) at this time was measured, and this value was used as the gas diffusibility in the planar direction.

<Measurement of the maximum height Rz of the surface of the microporous layer>

The method of measuring the maximum height Rz of the surface of the microporous layer is to use a laser microscope "VK-X100" (manufactured by KEYENCE Co., Ltd.) on the surface of the microporous layer of the gas diffusion electrode to be produced, and the objective lens is 20 times and the measurement area is 0.25. Measured by mm ² without cut off, and the maximum height Rz was obtained. At this time, in order to make the measured gas diffusion electrode not twist, it was cut into a square of 25 cm ² , and on the smooth glass substrate, four corners were attached and fixed with a tape from above. Further, the upper limit ‧ the lower limit of the laser focus distance is set to be a full range in which the height direction of the surface of the microporous layer of the gas diffusion electrode can be measured. Also, this measurement was performed on 4000 fields of view. The 4000 field of view measurement was measured from an area of 10 cm ² . Here, the maximum height Rz is the sum of the highest point (Rp) and the deepest trough depth (Rv) of the height information obtained by measuring the measured area by a laser microscope.

<Measurement of the maximum peak height Rp of the surface of the microporous layer>

The method of measuring the maximum peak height Rp of the surface of the microporous layer is first to form a coating film of the microporous layer coating on the smooth glass substrate using an applicator. The gap between the applicator and the glass substrate was set to be in a state of being pressed at a surface pressure of 0.15 MPa so that the thickness of the coating film measured by the micrometer was 40 μm. The coating film was dried at 23 ° C for 12 hours or more, and then a laser microscope "VK-X100" (manufactured by KEYENCE Co., Ltd.) was used, and the objective lens was 20 times and the measurement area was 0.25 mm ² . Peak height Rp. Moreover, this measurement was performed on 2000 fields of view. The measurement of the 2000 field of view was measured from an area of 5 cm ² . Here, the maximum peak height Rp is the highest point of the height information obtained by measuring the measurement area by a laser microscope.

<Measurement of crack occupancy on the surface of microporous layer>

The method for measuring the crack occupancy rate on the surface of the microporous layer was obtained by using a stereo microscope "Leica M205C" (manufactured by Leica Microsystems Co., Ltd.) with an eyepiece 10 times and an objective lens twice as long as the surface of the microporous layer of the gas diffusion electrode. The observation area was observed at 25 mm ² . The light source uses a ring light attached to the "Leica M205C" to fully illuminate, and the maximum amount of light vertically illuminates the surface of the microporous layer.

The observation conditions were a luminance of 50% and a gamma value of 0.60. Further, the observation field of view is 20 fields of view, and the 20 fields of view are selected from an area of 5 cm ² . The observation result of 20 fields of view is input by image, and binarized by the free image processing software "JTrim". The image is not subjected to processing other than binarization, and is binarized by the threshold 128. The black portion was judged to be a crack, the white portion was judged to be a non-crack portion, and the ratio of the number of black pixels in the total number of pixels was taken as the crack occupancy rate of the surface of the microporous layer.

<Measurement of gloss>

The method for measuring the gloss of the microporous layer coating is first to form a coating film of the microporous layer coating on the glass substrate using an applicator. The gap between the applicator and the glass substrate was set to be in a state of being pressed at a surface pressure of 0.15 MPa so that the thickness of the coating film measured by the micrometer was 40 μm. Apply the coat The film was dried at 23 ° C for 12 hours or more, and then the gloss was measured using a portable specular glossiness measuring device "Gloss Mobile GM-1" (manufactured by Suga Test Instruments Co., Ltd.). The measurement standard is based on JIS Z8741:1997 "Mirror Gloss - Measurement Method". The light of the gloss meter was set in parallel with the reflection direction of the applicator, and the respective portions of the surface of the coating film were measured at three points. Here, the average value of the obtained reflection angle of 85° is taken as the glossiness.

<Measurement of Viscosity of Microporous Layer Coatings>

In the viscosity measurement mode of the Bohlin Rotary Rheometer (specified by Spectris), a circular cone plate having a diameter of 40 mm and a inclination of 2° was used to increase the rotation speed of the cone plate and gradually measure the stress. At this time, the viscosity value of the shear rate of 17 s ^-1 was taken as the paint viscosity.

(Example 1)

The conductive fine particles CB1, the water-repellent resin D-210C, the surfactant, and the solvent were wetted and dispersed at a ratio shown in Table 1 using a stirring and mixing device (planetary mixer). The obtained coating was subjected to a pulverization step by passing through a three-roll mill once to obtain a microporous layer coating. The microporous layer coating material was applied to the surface of the carbon paper having a thickness of 100 μm obtained in the step A (1) by a die coating method to obtain a gas diffusion electrode. The composition, manufacturing conditions, and evaluation results of the microporous layer coating are shown in Table 1.

(Example 2)

In the pulverization step, a gas diffusion electrode was obtained in the same manner as in Example 1 except that the number of the minimum gap portions of the microporous layer coating material passing through the shearing portion of the apparatus was four. The results are shown in Table 1.

(Comparative Example 1)

A gas diffusion electrode was obtained in the same manner as in Example 1 except that the pulverization step was not carried out. As a result, the amount of aggregates was increased as compared with Example 1. The composition, manufacturing conditions, and evaluation results of the microporous layer coating are shown in Table 1.

(Example 3)

The conductive fine particles CB1, the surfactant, and the solvent were wetted by a stirring and mixing device (planetary mixer) and dispersed to obtain a coating material. The pulverization step is not performed. Further, D-210C, a surfactant, and a solvent of a water-repellent resin were further added to the obtained coating materials, and the mixture was diluted to obtain a microporous layer coating material as shown in the final coating composition of Table 1. The microporous layer coating material was applied to the surface of the carbon paper obtained in the step A(1) having a thickness of 100 μm by a die coating method to obtain a gas diffusion electrode. The composition, manufacturing conditions, and evaluation results of the microporous layer coating are shown in Table 1. The number of fields of view Rp and the number of fields of view Rz are increased as compared with the first embodiment.

(Comparative Example 2)

A gas diffusion electrode was obtained in the same manner as in Example 3 except that the composition of the diluted material was changed as shown in Table 1. The composition, manufacturing conditions, and evaluation results of the microporous layer coating are shown in Table 1. Compared with Example 3, the thickness of the microporous layer was reduced, and the penetration of the microporous layer coating material into the conductive porous substrate occurred, so that the gas diffusibility in the planar direction was lowered.

(Example 4)

The conductive fine particles CB2, the water-repellent resin ND-110, the surfactant, and the solvent were wetted and dispersed at a ratio shown in Table 2 using a stirring and mixing device (planetary mixer). The obtained coating was subjected to a pulverization step by passing through a mediumless grinding machine to obtain a microporous layer coating. Applying the microporous layer coating to the step A(1) by using a die coating method A carbon paper surface having a thickness of 100 μm was obtained as a gas diffusion electrode. The composition, manufacturing conditions, and evaluation results of the microporous layer coating are shown in Table 2.

(Comparative Example 3)

The gas diffusion electrode was obtained in the same manner as in Example 4 except that the shearing portion of the medium-free grinding machine used in the pulverization step was kept for 6 seconds in the minimum gap portion. The composition, manufacturing conditions, and evaluation results of the microporous layer coating are shown in Table 2. Compared with Example 4, the thickness of the microporous layer was reduced, and the penetration of the microporous layer coating material into the conductive porous substrate occurred, so that the gas diffusibility in the planar direction was lowered.

(Example 5)

The conductive fine particles of CB1 and VGCF, the water-repellent resin ND-110, the surfactant, and the solvent were wetted at a ratio shown in Table 2 using a stirring and mixing device (planetary mixer) to obtain a coating material. The obtained coating was subjected to a pulverization step by passing through a mediumless grinding machine to obtain a microporous layer coating. The microporous layer coating material was applied to the surface of the carbon paper having a thickness of 100 μm obtained in the step A (1) by a die coating method to obtain a gas diffusion electrode. The composition, manufacturing conditions, and evaluation results of the microporous layer coating are shown in Table 2.

(Comparative Example 4)

A gas diffusion electrode was obtained in the same manner as in Example 5 except that the minimum gap of the shear portion of the mediumless grinding machine used in the pulverization step was 600 μm. The composition, manufacturing conditions, and evaluation results of the microporous layer coating are shown in Table 2. The amount of condensate increased compared to Example 5.

(Comparative Example 5)

The same procedure as in Example 1 was carried out to obtain a microporous layer coating material. The micro The hole layer coating was applied to the surface of the carbon paper having a thickness of 200 μm obtained in the step A(2) by a die coating method to obtain a gas diffusion electrode. The composition, manufacturing conditions, and evaluation results of the microporous layer coating are shown in Table 2. The gas diffusibility in the thickness direction was lower than that in Example 1.

(Comparative Example 6)

The same procedure as in Example 1 was carried out to obtain a microporous layer coating material. The surface of the carbon paper having a thickness of 100 μm obtained in the step A(1) obtained by the microporous layer coating was applied by a die coating method so that the thickness of the microporous layer was 120 μm to obtain a gas diffusion electrode. The composition, manufacturing conditions, and evaluation results of the microporous layer coating are shown in Table 2. The gas diffusibility in the thickness direction was lower than that in Example 1.

(Example 6)

The microporous layer has a first microporous layer that contacts the conductive porous substrate and a second microporous layer that contacts the first microporous layer and is located on the outermost surface of the gas diffusion electrode.

The conductive fine particles CB1, the water-repellent resin D-210C, the surfactant, and the solvent were wetted at a ratio shown in Table 3 using a stirring and mixing device (planetary mixer) to obtain a coating material. The obtained coating material was subjected to a pulverization step by passing through a three-roll mill to obtain a first microporous layer coating material. The surface of the carbon paper having a thickness of 100 μm obtained in the step (1) of the first microporous layer coating was applied by a die coating method at a thickness of 35 μm to form a first microporous layer.

The coating liquid similar to the first microporous layer coating material was used as the second microporous layer coating material, and was applied to the surface of the first microporous layer at a thickness of 5 μm to form a second microporous layer to obtain a gas diffusion electrode. Microporous coating The composition, manufacturing conditions, and evaluation results are shown in Table 3.

(Example 7)

In the same manner as in Example 6, the surface of the carbon paper having a thickness of 100 μm obtained in the step (1) was formed into a first microporous layer with a thickness of 35 μm.

The conductive fine particles CB1, the surfactant, and the solvent were wetted at a ratio shown in Table 3 using a stirring and mixing device (planetary mixer) to obtain a coating material. The pulverization step is not performed. D-210C, a surfactant, and a solvent of a water-repellent resin were added to the coating at a ratio shown in Table 3, and diluted to obtain a second microporous layer coating represented by the final coating composition of Table 3. The solid content ratio after dilution was the same as in Example 4. The second microporous layer coating material was applied to the surface of the first microporous layer at a thickness of 5 μm to obtain a gas diffusion electrode. The composition, manufacturing conditions, and evaluation results of the microporous layer coating are shown in Table 3.

(Example 8)

In the same manner as in Example 6, except that the thickness of the first microporous layer was changed to 20 μm, the first microporous layer was formed on the surface of a carbon paper having a thickness of 100 μm.

The second microporous layer coating material was adjusted in the same manner as in Example 7 and applied to the surface of the first microporous layer at a thickness of 20 μm to obtain a gas diffusion electrode. The composition, manufacturing conditions, and evaluation results of the microporous layer coating are shown in Table 3. The crack occupancy rate is increased compared to Example 7.

(Example 9)

In the same manner as in Example 6, except that the thickness of the first microporous layer was changed to 5 μm in the same manner as in Example 6, the first microporous layer was formed on the surface of the carbon paper having a thickness of 100 μm.

The second microporous layer coating material was adjusted in the same manner as in Example 7 and applied to the surface of the first microporous layer at a thickness of 35 μm to obtain a gas diffusion electrode. The composition, manufacturing conditions, and evaluation results of the microporous layer coating are shown in Table 3. The crack occupancy rate is increased compared to Example 7.

(Embodiment 10)

In the same manner as in Example 6, the surface of the carbon paper having a thickness of 100 μm obtained in the step (1) was formed into a first microporous layer with a thickness of 35 μm.

The conductive fine particles CB1, the surfactant, and the solvent were wetted at a ratio shown in Table 3 using a stirring and mixing device (planetary mixer) to obtain a coating material. The pulverization step is not performed. The coating was diluted with D-210C, a surfactant, and a solvent added to the water-repellent resin in the ratio shown in Table 3 to obtain a second microporous layer coating represented by the final coating composition of Table 3. The solid content ratio after dilution was the same as in Comparative Example 2. The second microporous layer coating material was applied to the surface of the first microporous layer at a thickness of 5 μm to obtain a gas diffusion electrode. The composition, manufacturing conditions, and evaluation results of the microporous layer coating are shown in Table 3.

(Example 11)

In the same manner as in Example 6, the surface of the carbon paper having a thickness of 100 μm obtained in the step (1) was formed into a first microporous layer with a thickness of 35 μm.

The conductive fine particles CB2, the water-repellent resin ND-110, the surfactant, and the solvent were wetted at a ratio shown in Table 4 using a stirring and mixing device (planetary mixer) to obtain a coating material. The coating was subjected to a pulverization step by passing through a mediumless grinding machine to obtain a second microporous layer coating material. The coating residence time of the minimum gap portion of the sheared portion of the apparatus used in the pulverization step was 6 seconds. The second microporous layer coating was first The surface of the microporous layer was coated with a thickness of 5 μm to obtain a gas diffusion electrode. The composition, manufacturing conditions, and evaluation results of the microporous layer coating are shown in Table 4.

(Embodiment 12)

The first microporous layer coating material was obtained in the same manner as in Example 6 except that the pulverization step was not carried out. The surface of the carbon paper having a thickness of 100 μm obtained in the step (1) of the first microporous layer coating was applied by a die coating method at a thickness of 35 μm to form a first microporous layer.

The second microporous layer coating material was adjusted in the same manner as in Example 6, and was applied to the surface of the first microporous layer to a thickness of 5 μm to obtain a gas diffusion electrode. The composition, manufacturing conditions, and evaluation results of the microporous layer coating are shown in Table 4.

(Example 13)

In the same manner as in Example 12, the surface of the carbon paper having a thickness of 100 μm obtained in the step (1) was formed into a first microporous layer with a thickness of 35 μm.

The second microporous layer coating material was adjusted in the same manner as in Example 7 and applied to the surface of the first microporous layer at a thickness of 5 μm to obtain a gas diffusion electrode. The composition, manufacturing conditions, and evaluation results of the microporous layer coating are shown in Table 4.

(Example 14)

In the same manner as in Example 12, the surface of the carbon paper having a thickness of 100 μm obtained in the step (1) was formed into a first microporous layer with a thickness of 35 μm.

The second microporous layer coating material was adjusted in the same manner as in Example 10, and applied to the surface of the first microporous layer at a thickness of 5 μm to obtain a gas diffusion electrode. The composition, manufacturing conditions, and evaluation results of the microporous layer coating are shown in Table 4.

(Example 15)

In the same manner as in Example 12, the surface of the carbon paper having a thickness of 100 μm obtained in the step (1) was formed into a first microporous layer with a thickness of 35 μm.

The second microporous layer coating material was adjusted in the same manner as in Example 11 and applied to the surface of the first microporous layer at a thickness of 5 μm to obtain a gas diffusion electrode. The composition, manufacturing conditions, and evaluation results of the microporous layer coating are shown in Table 4.

The "minimum gap" in the table indicates the minimum gap of the cut portion of the device used in the pulverization step.

The "residence time" in the table indicates the residence time of the coating of the minimum gap portion of the sheared portion of the apparatus used in the pulverization step.

The "number of passes" in the table indicates the number of times the coating passes through the minimum gap portion of the cut portion of the device used in the pulverizing step.

In the table, the "number of fields of view Rp" indicates the number of fields of view in which the maximum peak height Rp is 10 μm or more in the 2000 field of view when the surface of the microporous layer is observed at an area of 0.25 mm ² .

In the table, the "field of view Rz" indicates the number of fields of view in which the maximum height Rz is 50 μm or more in the 4000 field of view when the surface of the microporous layer is observed at an area of 0.25 mm ² .

201‧‧‧ paint

202‧‧‧cutting section

203‧‧‧Rolling direction of the drum

204‧‧‧Minimum clearance

205‧‧‧Roller

Claims (15)

A gas diffusion electrode is a gas diffusion electrode having a microporous layer on at least one surface of a conductive porous substrate, wherein the gas diffusion electrode has a thickness of 30 μm or more and 180 μm or less, and the microporous layer has a thickness of 10 μm or more and 100 μm or less. When the surface of the microporous layer is observed with an area of 0.25 mm ² and 4000 fields of view, the number of fields of view having a maximum height Rz of 50 μm or more in the 4000 fields of view is 0 or more fields and 5 fields or less. The gas diffusion electrode according to claim 1, wherein the microporous layer is composed of a first microporous layer contacting the conductive porous substrate and a second microporous layer contacting the first microporous layer and located on the outermost surface of the gas diffusion electrode. Composition. The gas diffusion electrode according to claim 2, wherein the thickness of the first microporous layer is 9.9 μm or more and less than 100 μm, and the thickness of the second microporous layer is 0.1 μm or more and less than 10 μm. The gas diffusion electrode according to any one of claims 1 to 3, which has a gas diffusibility in a thickness direction of 30% or more. The gas diffusion electrode according to any one of claims 1 to 4, wherein when x (μm) is the thickness of the gas diffusion electrode and e is a Napier's constant, the gas diffusion in the plane direction is 0.7e ^0.025x. (cc/min) or more. The gas diffusion electrode according to any one of claims 1 to 5, wherein the microporous layer contains conductive fine particles and a water repellent resin. The gas diffusion electrode of claim 6, wherein the conductive fine particles comprise a conductive material having a linear portion. The gas diffusion electrode according to any one of claims 1 to 7, wherein a crack occupancy ratio of the surface of the microporous layer is 0% or more and 0.072% or less. A microporous layer coating material comprising a microporous layer coating containing conductive microparticles and a solvent, wherein the surface of the coating film formed by coating the microporous layer coating on a glass substrate is 2000 fields of view when the area is 0.25 mm ² , in the 2000 field of view The field of view with a maximum peak height Rp of 10 μm or more is 0 or more and 25 or less, and the gloss is 1% or more and 30% or less. The microporous layer coating of claim 9 has a viscosity of 2 Pa ‧ or more and 15 Pa ‧ or less. A method for producing a microporous layer coating material according to claim 9 or 10, which comprises the steps of: wetting the conductive fine particles in a solvent, dispersing the wetting, dispersing the steps, and pulverizing the agglomerates in the coating obtained by the wetting and dispersing step The comminution step. The method for producing a microporous layer coating according to claim 11, wherein the viscosity of the coating after the wetting and dispersing step and before the pulverizing step is 5 Pa ‧ or more and 300 Pa ‧ or less. The microporous layer coating manufacturing method according to claim 11 or 12, wherein the apparatus for pulverizing in the pulverizing step has a minimum gap of the sheared portion of 10 μm or more and 500 μm or less. The method for producing a microporous layer coating according to any one of claims 11 to 13, wherein the apparatus for pulverizing in the pulverizing step has a coating retention time of a minimum gap portion of the sheared portion of more than 0 second and 5 seconds or less. The microporous layer coating manufacturing method according to any one of claims 11 to 14, wherein the apparatus for pulverizing in the pulverizing step is one pass.